The present invention relates generally to a subscriber identity module detachably loaded on the main body of a mobile communication terminal device for identifying subscribers and, more particularly, to a method of preventing access to this subscriber identity module for data at the time of its loss by mistake or theft.
In the pan-European Digital Cellular System (hereafter referred to as GSM (Global System for Mobile communications), the subscriber identity module (SIM) is used in each GSM-compliant mobile communication terminal device (hereafter simply referred to as a mobile terminal or a terminal) to enhance security. SIM, having data processing and storage capabilities, is a card-shaped device that is detachably loaded in the terminal device for GSM subscriber identification. When the user loads SIM into a terminal device and enters PIN (Personal Identification Number), the communication and other capabilities of the mobile terminal become effective. However, the user sometimes feels bothersome when prompted to enter PIN every time the terminal device is powered on, thereby making the user to use the mobile phone with the PIN authentication function disabled. If the mobile phone with the PIN authentication function disabled is lost by mistake or theft, the party in possession of the lost mobile terminal can communicate by using it in complete disregard of user's intention.
To prevent such problem from happening, an authentication center (AuC) is set up in the GSM system. The authentication center has a subscriber list that contains the correlations between user IMSI (International Mobile station Subscriber Identity) and user phone number. If the user whose mobile terminal has been lost reports thereof, the correlation in the subscriber list is changed to reject the calls originated by the lost mobile terminal. Namely, the user notifies the authentication center with which his IMSI is registered of the loss of user's mobile terminal to have a new IMSI issued, thereby preventing the mobile terminal having the lost IMSI from establishing communication by a third person through the appropriate processing by the base station.
However, SIM stores personal data, such as AND (Abbreviated Dial Number) and FDN (Fixed Dial Number), for example. With the PIN authentication function disabled on the lost SIM, the personal data is ready for reading from the SIM on any mobile terminal.
This problem also exists with UIM (or USIM) that is adopted on the third-generation mobile phone system.